The present invention relates to an impacting device that utilizes an impact action produced by magnetostriction.
Heretofore, in impact machines, such as a breaker for crushing concrete or a rock with impacts or a drill for drilling a rock with impacts, the impacting device for imparting impacts to the impact-transmitting tool, a chisel or a rod, for example, has used blows of a piston operated by hydraulic or pneumatic force.
However, in the impacting device such as this, a shock wave (a stress wave, namely, an elastic strain wave) occurs in the impact-transmitting tool, as a result of a blow of the piston, and this shock wave travels toward an object, which is thereby crushed and therefore the sound of a blow and the reaction and vibration resulting from acceleration of the piston have been unavoidable.
When a shock wave is produced, it is necessary to follow a series of processes: electric energy is changed into mechanical energy by a motor, the mechanical energy is changed into kinetic energy of the piston by a hydraulic pump, for example, and the kinetic energy is changed into strain energy of the impact-transmitting tool by a blow of the piston, thus producing a shock wave. The energy efficiency has not been so high.
To make the piston having a large inertial resistance reciprocate at high speed, the accelerating force by hydraulic or pneumatic pressure has not been sufficient and there is a limit to increasing the number of blows, so that it has been not easy to increase output.
It has been known that there is a best waveform of a shock wave adequate for the crushing characteristics (penetration resistance) of each object. Unless the waveform of the shock wave is adequate, the impact-transmitting tool is unable to attain sufficient penetration into the object, reducing the crushing efficiency and increasing reflection of the shock wave from the object which partly contributes to increasing effects to the impacting device and reducing the durability of the impact machine. To control the waveform of a shock wave, measures have been taken, such as changing the shape of the piston to suit an object, but changing the piston shape is troublesome indeed.
The present invention has been made to solve the above problems and has as its object to provide an impacting device for crushing and drilling with low noise and vibration, which features high crushing efficiency, improved energy efficiency, high output and prolonged durability.
In the impacting device according to the present invention, the above problems have been solved by arranging a super magnetostrictive material in the center of the exciting coil to which a pulse voltage is applied, arranging an impact transmitting tool in contact with the front end of the super magnetostrictive material, and placing a reaction-receiving plate in contact with the other end of the super magnetostrictive material.
Magnetostriction is a phenomenon whereby the outside diameter dimension of a ferromagnetic body, such as iron, changes when it is magnetized. In contrast to strain of magnetic metals, which is no more than 10xe2x88x925 to 10xe2x88x926, magnetostrictive materials exhibit strain on the order of 10xe2x88x923 by magnetostriction.
In this impacting device, a pulse voltage is applied to an exciting coil, and by an exciting current flowing in the exciting coil, the super magnetostrictive material is given changes of magnetic field so that the super magnetostrictive material produces such magnetostriction as to give a desired impact waveform. The impacting device transmits the shockwave through the impact-transmitting tool to an object, which is thereby crushed.
The impacting device according to the present invention converts electric energy directly into strain energy and therefore has a high energy efficiency ratio. And, because it does not require hydraulic equipment, hydraulic piping and complicated mechanical devices, such as a hydraulic striking mechanism, this impacting device makes it possible to simplify the impact machine.
To make the impact-transmitting tool penetrate into an object, such as a rock, with energy of a shock wave, it is necessary to maintain the displacement speed higher than a certain speed and longer than a certain period of time. Objects of rock and stone to be crushed are diverse in physical properties and therefore they have various levels of penetration resistance. To ensure an amount of penetration greater than a certain value and to limit required power to a certain value or less, based on the facts that strain by magnetostriction is proportional to the strength of a magnetic field, namely, the magnitude of an exciting current and that the temporal change rate of strain is equal to displacement speed, a pulse voltage is repeatedly applied to the exciting coil such that the exciting current of the exciting coil increases with passage of a voltage-applied time and after reaching a desired maximum value, suddenly drops to zero. Consequently, the super magnetostrictive material reaches desired displacement and displacement speed in its deformation by magnetostriction. The pulse width at this time is suitably selected from a range of several tens of xcexcs up to several hundreds of xcexcs, while the pulse interval is suitably selected from a range of several ms up to several hundreds of ms.
When carrying out penetration of the impact-transmitting tool, the leading end of it is preferably in contact with an object. If the leading end of the impact-transmitting tool is not in contact with the object, the shock wave returns as a tensile stress wave through the impact-transmitting tool, making it impossible to effectively transmit energy to the object. For this reason, it is necessary to have the whole impact-transmitting tool statically pressed against the object.
If a pulse voltage is applied to the exciting coil such that the exciting current of the exciting coil increases with passage of the voltage-applied time, and after reaching a desired maximum value, maintains the maximum value for a specified time, so long as the exciting current maintains a fixed value, the super magnetostrictive material is prolonged and the impact-transmitting tool can be pressed against the object. The time for maintaining the exciting current at a fixed value is suitably selected from a range less than several tens of ms.
To make effective use of a shock wave for penetration work of the impact-transmitting tool into the object, it is important to minimize the occurrence of reflected waves.
If a pulse voltage is applied to the exciting coil such that the exciting current of the exciting coil increases in proportion to an elapsed time squared or approximately as a logarithmic function during passage of a voltage-applied time from the initial value to the maximum value, then the occurrence of reflected waves can be reduced.
If a detection coil is provided adjacent to the exciting coil and if, on arrival of a reflected wave at the super magnetostrictive material from the impact-transmitting tool, changes in the current or voltage produced by magnetostriction are measured by the detection coil and the waveform of the reflected wave is detected by a detection unit and the magnitude of an incident wave in the penetration process of the impact-transmitting tool into the object is adjusted according to the reflected wave, then the occurrence of reflected waves can be reduced, which makes it possible to improve the penetration efficiency and decrease vibration and reaction.